When an abnormal reaction occurs in a region where a reaction occurs (hereinafter, simply referred to as the “reaction region”), and unreacted particles are mixed or the reaction becomes incomplete, there is a large influence on an action of an engine of operating with utilizing the reaction. For example, in the case where premixing of hydrocarbon fuel and the air is not performed, incomplete combustion is generated in a region where the fuel is rich so as to form soot and generate a luminous flame. When unexpected combustion is generated in a combustion chamber in an internal combustion engine, so-called knocking is generated. Detecting generation of such an abnormal reaction and knowing what kind of characteristic the reaction has by measurement and an analysis are essential for making the engine of operating with utilizing the reaction highly efficient and more environmentally friendly.
Conventionally, as a method for detecting reaction abnormality and knowing the characteristic of the reaction, there are an experimental method by human perception, a method by pressure measurement and a pressure analysis of the reaction region, a method by measurement and an analysis of sound or vibration of a reaction chamber, a method of measuring exhaust and the like from the reaction region and analyzing a component thereof and the like. However, since these methods are sensory or indirect methods, reproducibility of detection is not enough and detailed information on the reaction cannot be obtained.
Therefore, there are various proposed techniques such as a technique detecting the generation of the reaction abnormality by directly and optically measuring the reaction region, and a technique obtaining information on a state of the reaction and the like by analyzing light in the region where the reaction is generated. For example, Patent Literature 1 discloses a method comprising: installing an optical sensor in a combustion chamber in correspondence to each self-emitting light of a flame, calculating an air-fuel ratio from a ratio of emission intensity detected by the optical sensor, and diagnosing combustion based on this air-fuel ratio. Alternatively, like a combustion diagnosing method described in Non-patent Literature 2, there is a method comprising: inserting an optical fiber into a combustion chamber, detecting light in the combustion chamber via the optical fiber, and detecting combustion abnormality such as knocking by intensity of the light.
The present inventors propose an optical measurement apparatus described in Patent Literature 2. This optical measurement apparatus is to measure light generated by physical and chemical reactions in a local place in a combustion chamber with using a plug having an optical element forming a reflecting optical system, detect and analyze physical and chemical reaction regions and local physical and chemical reaction characteristics.
[Patent Literature 1] Japanese Patent Laid-Open No. 2005-226893
[Patent Literature 2] Japanese Patent Laid-Open No. 2006-292524
[Non-patent Literature 1] AVL Visiolution Catalog (AVL Japan)